As a NAND flash memory, there is proposed a three-dimensionally stacked memory formed by a collective process so as to be stacked in the vertical direction to suppress an increase in the process cost.
In the three-dimensionally stacked memory, a cylindrical hole (memory hole) is formed at once in a plurality of electrodes stacked on a semiconductor substrate. A memory film is formed on the inner wall of the hole, and a polysilicon film (semiconductor pillar) serving as a channel is then formed inside the hole. NAND strings (memory strings) each formed from a plurality of MONOS memory cells connected in series in the stacking direction can thus be formed at once.
There is also proposed a collectively processed three-dimensionally stacked memory using, as a channel, a U-shaped semiconductor pillar formed from a pair of pillar portions and a connection portion that connects the pillar portions at the lower end. In this case, memory strings are formed along the U-shaped semiconductor pillars.